Admixture for hydraulic cement

ABSTRACT

The present invention is a specific combination of components having unique properties both in composition and benefits. Such a combination has been found in alkali or alkaline earth metal nitrates, alkanolamines and alkali or alkaline earth metal thiocyanates. In such combinations it has also been found that alkaline and alkali earth thiosulfates and chlorides below the concentration level where corrosion is promoted may advantageously be substituted for all or part of the thiocyanates and that diethanolamine, N,N-di(hydroxyethyl)glycine (bicine) and N,N-di(hydroxyethyl)-β-aminopropionic acid (DAPA) and certain alkanolamines and alkanolamino acids and derivatives may advantageously be substituted for all or part of the triethanolamine.

BACKGROUND OF THE INVENTION

This invention relates to admixture compositions for incorporation intohydraulic cement mixes, such as concretes, mortars and grouts and drymixes for making these, to provide economy, compressive strengthbenefits at all ages, and a desirable degree of acceleration of rate ofhardening and setting.

The use of chemical admixtures to achieve these effects is well known inthe art. For example, calcium chloride is well known as an economic andeffective accelerator, but has the disadvantage of promoting corrosionof metal embedments at certain dosages, as well as other disadvantages.Thus, there is a need for economical and effective agents to replacecalcium chloride in this application, and this has promoted a continuingsearch on the part of the industries involved.

Thus, U.S. Pat. No. 3,782,991 issued to Burge discloses anhydrousaluminum sulfate to increase early compressive strength of buildingmaterials, together with triethanolamine as a set accelerator.

Also, U.S. Pat. No. 4,298,392 issued to Isselmann discloses an admixturecomprised of a combination of silica sol and sodium thiocyanate employedto increase compressive strength of cementitious systems prior to 72hours. However, his data show that the desired effect is not achieved bythe thiocyanate alone, but only by the combination.

In addition, U.S. Pat. No. 4,256,500 issued to Turpin discloses avariety of inorganic compounds for use in cementitious systemscontaining pozzolanic materials in order to obtain cement compositionsmore economical than compositions of equivalent compressive strengththat previously have been employed. The chemical agents employed aloneor in combination include alkali thiosulfate, sulfate, sulfite, nitrate,nitrite, thiocyanate, cyanide, chlorides and others. Superior effectswere secured by combinations of sodium thiocyanate and sodiumthiosulfate as shown in Turpin's Table 12, but even more complexmixtures yielded good results as shown in his Table 13 for sodiumnitrate plus sodium thiosulfate, plus sodium sulfite plus sodiumsulfate.

There is also U.S. Pat. No. 4,337,094 issued to Tokar disclosing as anaccelerator for cementitious systems and also to improve compressivestrength, a combination of calcium nitrate in the range of 0.5 to 3.0%based on weight of cement and an alkanolamine, with or without minoramounts of gluconates or lignosulfonates.

U.S. Pat. No. 4,373,956 issued to Rosskopf discloses an admixtureconsisting of an alkali or alkaline earth or ammonium salt of thiocyanicacid in combination with an alkanolamine which when added to acementitous mix will increase the rate of hardening of the mix and willincrease the compressive strength of the mix after hardening.

The art just cited approaches the goal of securing a desired degree ofacceleration of rate of set of cementitious systems without sacrifice toeither early or ultimate compressive strength, but still greaterbenefits of this type are desired than are possible with use of theadmixtures thus far developed. Therefore, it would be highlyadvantageous to develop an admixture which would accelerate the rate ofhardening and increase compressive strength of the hardened mix to astill greater degree, and to do so in an economical manner.

SUMMARY OF THE INVENTION

The present invention is a specific combination of components havingunique properties both in composition and benefits. Such a combinationhas been found in alkali or alkaline earth metal nitrates, alkanolaminesand alkali or alkaline earth metal thiocyanates. In such combinations ithas also been found that alkaline and alkali earth thiosulfates andchlorides below the concentration level where corrosion is promoted mayadvantageously be substituted for all or part of the thiocyanates andthat diethanolamine, N,N-di(hydroxyethyl)glycine (bicine) andN,N-di(hydroxyethyl)-β-aminopropionic acid (DAPA) and certainalkanolamines and alkanolamino acids and derivatives may advantageouslybe substituted for all or part of the triethanolamine. The lattercompounds are illustrative of a class of compounds that may be preparedby an addition reaction between an activated olefin and secondaryamines, as follows: ##STR1## alternatively, such compounds may beprepared as illustrated in the following generalized reaction: ##STR2##where R₁ and R₂ are hydrogen or methyl, X is a carboxylic acid and itslower alkyl esters, nitrile, amide and N-substituted amide, Y is H or X,and Z is X, alkali or alkanolamine carboxylate salt and R₃ is H, --CH₂--CH₂ --OH or ##STR3## and R₄ is --CH₂ --CH₂ --OH or ##STR4##

In addition, in the above equations, when Z=X=CO₂ H one obtains itaconicacid, which when reacted as the monosodium salt with diethanolamineyields N,N-di(hydroxyethylamino)methyl succinic acid, monosodium salt,which has been found to be highly effective in enhancing compressivestrength and in accelerating rate of hardening of cementitious mixes.

Mixtures of these in specific ranges of absolute amounts and relativeproportions incorporated into cementitious systems have been found toyield beneficial effects on rate of hardening of cementitious mixes andon early and ultimate compressive strength after hardening, surprisingin degree and due to interactive effects not predictable by one skilledin the art.

It is therefore an object of the present invention to provide improvedhydraulic cement mixes, such as portland cement mixes, mortars andgrouts by incorporation of a specified admixture before, after or duringaddition of water.

It is another object of this invention to provide improved hydrauliccement mixes, such as portland cement mixes, including concrete, mortarand grout mixes, neat cement mixes, nonplastic cement mixes, and drymixes, which include an admixture which will advantageously acceleratethe rate of hardening and setting of the cement mix and increase theearly compressive strength.

The invention comprises a hydraulic cement mix including hydrauliccement, aggregate, sufficient water to effect hydraulic setting of thecement and an additive comprising a mixture of an alkali or alkalineearth or ammonium salt of thiocyanic acid, an alkanolamine and analkali, alkaline earth or ammonium salt of nitric acid, andcorresponding mixtures in which alkali or alkaline earth thiosulfatesand chlorides below the level where corrosion is promoted aresubstituted for some or all of the . .nitrate.!. .Iadd.thiocyanate.Iaddend.and certain alkanolamino acids and their water soluble saltsare substituted for the alkanolamine, the additive being present in anamount sufficient to increase the rate of hardening of the mix and thecompressive strength of the hardened mix. The admixture is preferablyselected from the group comprising sodium, potassium, ammonium, calciumor magnesium thiocyanate in combination with triethanolamine andammonium, sodium, potassium, calcium or magnesium nitrate and thesubstitutions just cited and is present in a total amount up to about3.0% by weight based on the weight of cement, generally in an amountbetween about 0.10% and 2.0% by weight based on weight of cement andpreferably the three components being in the following ranges or weightpercent of cement: the nitrate, 0.05% to 2.0%; the alkanolamine, 0.005%to 0.08%; and the thiocyanate, 0.01% to 0.50%. Use of this additive inthe preferred ranges of its components results in an acceleration ofrate of hardening as well as an increase in compressive strength of thecementitious system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of this invention the term "hydraulic cement" isintended to include all cementitious compositions capable of hardeningby the action of water, but the preferred use is in portland cementmixes, with or without interground or interblended pozzolanic materials.

The salts of the thiocyanic acid have the general formula

    M(SCN).sub.X

where M is an alkali metal or ammonium radical or an alkaline earthmetal and where X is 1 for alkali metal salts and 2 for alkaline earthsalts. These salts are variously known as sulfocyanates, sulfocyanides,rhodanates or rhodanide salts. Alkanolamine is a generic term for agroup of compounds in which trivalent nitrogen is attached directly to acarbon atom of an alkyl alcohol and examples are monoethanoalamine,diethanolamine and triethanolamine. The alkanolamino acids and theirderivatives that may be substituted for the alkanolamines are describedabove.

The thiosulfate salts that may be substituted in part or entirely forthe thiocyanates have the general formula

    M.sub.X (S.sub.2 O.sub.3)

where M is alkali metal or an alkaline earth metal and X is 2 for alkalimetal and ammonium salts and 1 for alkaline earth sales.

The salts of nitric acid have the general formula

    M(NO.sub.3).sub.X

where X is 1 for alkali metal salts and 2 for alkaline earth salts, andM has the meaning indicated above.

In the practice of the present invention, the three components describedabove are incorporated into hydraulic cement mixes in amounts sufficientto accelerate the rate of hardening and setting of the mixes and toincrease compressive strength after hardening. The admixture ispreferably incorporated into the mix as an aqueous solution comprising aportion of the water used in mixing the hydraulic cement, aggregate, andwhere desired, pozzolanic material. The term includes both fineaggregate such as sand and coarse aggregate such as gravel as is commonin the art. The proportion of fine and coarse aggregate will varydepending on the desired properties of the mortar or concrete. Theamount of water generally should be enough to effect hydraulic settingof the cement component and to provide a desired degree of workabilityto the mix before hardening.

For the purpose of illustrating the advantages obtained by the practiceof the present invention, plain concrete mixes were prepared andcompared with similar mixes containing the admixture described above.The same type and brand of cement was used in each test series and thekinds and proportions of aggregates were held substantially constant.The methods and details of testing were in accordance with currentapplicable ASTM standards, and in each series of tests the individualmixes were on a comparable basis with respect to cement content anddegree of workability as measured in accordance with ASTM C 143-78. Thetests were made with all materials at about 70° F. (21° C.), with a sandto coarse aggregate weight ratio of 0.48±0.01 and a cement content inthe mix of 420 lbs. per cubic yard (249 kg/m³).

Data in Table I show that modest benefits are secured in terms ofacceleration and compressive strength increases at all ages tested withthe particular dosage of calcium nitrate chosen, as was to be expected.Addition of the specified dosage of triethanolamine to the calciumnitrate admixture further increased these benefits. Addition of thethird component, the thiocyanate, still further increased thesebenefits. However, doubling the amounts of the first two components,other things being equal (comparing Mix 5 with Mix 4), while stillfurther increasing most benefits, did so only modestly when one comparestotal admixture dosages (0.56 for Mix 4 and 1.07 for Mix 5), andactually decreased the early or one-day compressive strength. Insummary, the data show a beneficial additivity of the three admixturecomponents, with unexpected benefits at relatively low dosages, whichwould translate to greater cost-effectiveness. This effect is moreclearly shown in Table II, where the same cement, mix design and testconditions were employed, except that 7 day and 28 day compressivestrength tests were not made, and sodium nitrate was used in lieu ofcalcium nitrate. In comparing Mix 7 and Mix 8 one sees that verysignificant decreases in the nitrate and amine components unexpectedlygave comparable benefits.

                  TABLE I    ______________________________________                  Time of                  Set Relative                  To Plain    Admixture, Wt.                  Mix (Hrs)  Compressive Strength,    Mix  percent of cement                      Initial Final                                   psi (MPa)    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    1.   None         6 3/4   9 3/8                                   540   2169  3404                                   (3.7) (15.0)                                               (23.5)    2.   Ca(NO.sub.3).sub.2, 0.50                      6 1/2   8 1/2                                   548   2335  3549                                   (3.8) (16.1)                                               (24.5)    3.   Ca(NO.sub.3).sub.2, 0.50 +                      5 3/8   7 1/2                                   583   2470  3941         triethanolamine,          (4.0) (17.0)                                               (27.2)         0.01    4.   Ca(NO.sub.3).sub.2, 0.50 +                      5 1/8   7    721   2667  4052         triethanolamine,          (5.0) (18.4)                                               (27.9)         0.01 + NaCNS,         0.05    5.   Ca(NO.sub.3).sub.2, 1.00 +                      4 5/8   6 1/2                                   686   2820  4155         triethanolamine,          (4.7) (19.4)                                               (28.6)         0.02 + NaCNS,         0.05    ______________________________________

                  TABLE II    ______________________________________                    Time of Set                    Relative To                    Plain Mix                             Compressive                    (Hrs)    Strength,    Mix  Admixture, Wt percent of                          Initial Final                                       psi (MPa)    No.  cement on solid basis                          Set     Set  1-day    ______________________________________    6.   None             5 1/8   7 1/2                                       1079                                       (7.4)    7.   NaNO.sub.3, 0.25 +                          4 1/4   6    1435         triethanolamine, 0.015 +      (9.9)         NaCNS, 0.03    8.   NaNO.sub.3, 0.40 +                          3 7/8   5 1/2                                       1422         triethanolamine, 0.023 +      (9.8)         NaCNS, 0.03    ______________________________________

It is apparent that Mix 7 would be a highly cost-effective admixture byvirtue of significant benefits at low total dosage, in this case lessthan 0.3% of cement. This is better appreciated in light of the factthat the best known inorganic accelerator, namely, calcium chloride,commonly is used at the dosage of 2.0% by weight of the cement. However,unexpectedly, it is possible to go still further in low-dosageeffectiveness, as long as the three components are used in combination,as illustrated by data in Table III. The tests were made under the sameconditions and with the same cement as was used to secure the foregoingdata. Here and in all subsequent tables, values relative tocorresponding values for a within-group plain mix, rather than absolutevalues, are shown. The time of set relative values are preceeded by aplus (+) or minus (-) sign. The minus sign indicates earlier settingthan the plain mix, or acceleration. A plus sign indicates a delayedtime of set relative to the plain mix, or a retardation.

                  TABLE III    ______________________________________                    Time of Set                    Relative To                             Compressive                    Plain Mix                             Strength, % of                    (Hrs)    Within-group    Mix  Admixture, Wt percent of                          Initial Final                                       plain mix    No.  cement on solid basis                          Set     Set  1-day 3-days    ______________________________________     9.  NaNO.sub.3, 0.10 +                          -1      -1 1/2                                       138   127         NaCNS, 0.05 +         triethanolamine, 0.015    10.  NaNO.sub.3, 0.10 +                          -7/8    -1 1/2                                       131   119         NaCNS, 0.03 +         triethanolamine, 0.005    ______________________________________

In Table III, Mix 9 employs less than 0.17% total dosage and Mix 10,less than 0.14% total dosage, based on weight of cement. The magnitudesof the beneficial effects secured at these dosages are remarkable andunexpected. This is a dosage range an order of magnitude lower thancommonly is used with known inorganic accelerators employed alone orwith triethanolamine.

In Table I data were presented to show the need of each of the threecomponents by successive addition. The reverse process of subtractionwas used to show the significant role of the thiocyanate component intests shown in Table IV. These tests were made with the same brand ofcement and same test conditions as all tests previously described.

                  TABLE IV    ______________________________________                    Time of Set                    Relative to                             Compressive                    Plain Mix                             Strength, % of                    (Hrs)    Within-group    Mix  Admixture, Wt percent of                          Initial Final                                       plain mix    No.  cement on solid basis                          Set     Set  1-day    ______________________________________    11.  NaNO.sub.3, 0.25 +                          -1 1/8  -1 3/4                                       149         NaCNS, 0.03 +         triethanolamine, 0.015    12   NaNO.sub.3, 0.23 +                          -1 1/8  -1 1/2                                       122         triethanolamine, 0.015    ______________________________________

The data in Table IV show that in the three component combination, thecontribution of the thiocyanate is mainly to early compressive strength.The contribution of this magnitude at the low dosage of 0.03 weightpercent of cement is remarkable and unexpected.

Although the composite admixture of this invention is economically mosteffectively used at low dosages as shown above, it remains highlybeneficial to concrete when employed at high dosages, as shown by thedata in Table V. These tests were made in the same manner and under thesame circumstance as those previously described, except that a differentbrand of cement was used.

                  TABLE V    ______________________________________                    Time of Set                    Relative to                             Compressive                    Plain Mix                             Strength, % of                    (Hrs)    Within-group    Mix  Admixture, Wt percent of                          Initial Final                                       plain mix    No.  cement on solid basis                          Set     Set  1-day    ______________________________________    13.  NaNO.sub.3, 0.50 +                          -1 1/8  -1 1/2                                       145         triethanolamine, 0.01 +         NaCNS, 0.05    14.  NaNO.sub.3, 1.00 +                          -1 3/8  -1 7/8                                       160         triethanolamine, 0.02 +         NaCNS, 0.10    15.  NaNO.sub.3, 2.00 +                          -1 3/8  -2   174         triethanolamine, 0.04 +         NaCNS, 0.20    ______________________________________

It may be noted that the dosages of the mixes shown in Table V are ageometric progression, with the dosage of each component in each mixbeing just double corresponding dosages in the prior mix. While eachcomposite admixture is highly beneficial and acceleration and earlystrength of the concrete increases with increasing dosage, themagnitudes of these improvements are very modest for a test series wheredosage is increasing geometrically. Clearly, limiting values of thepossible improvements in this context are being approached.

Further tests were made in the same manner and under the same conditionsas previously described. In Table VI below are shown the beneficialeffects secured by using as the sole admixture DAPA(di(hydroxyethyl)-β-aminopropionic acid) and certain adducts thereof.

                  TABLE VI    ______________________________________                  Time of                  Set Relative                  To Plain   Compressive Strength,    Admixture, Wt.                  Mix (Hrs)  % of    Mix  percent of cement                      Initial Final                                   Within-group plain mix    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    16.  DAPA, 0.05   -3/8    -3/4 109   110   105    17.  α-methyl DAPA,                      -3/8    -3/4 113   112   112         0.05    18.  calcium salt of         α-methyl DAPA,                      -1/4    -5/8 107   108   101         0.01 +         α-methyl DAPA,                      -1/4    -1/2 108   113   104         0.025 +         α-methyl DAPA,                      -3/8    -3/4 113   114   112         0.050 +         α-methyl DAPA,                      -5/8    -1   110   112   110         0.100 +    ______________________________________

Data of Table VI show that the alkanolamino acid type of material mayproduce accelerating and strength-enhancing effects that increase withincreasing dosage over a significant range. This contrasts favorablywith widely-used triethanolamine, the accelerating effects of which aremore severely dosage-limited. This effect may be readily seen bycontrasting data of Table VI with data of Table VII, wherein thecorresponding tests were made under the same conditions, including thesame brand of cement.

                  TABLE VII    ______________________________________                  Time of                  Set Relative                  To Plain   Compressive Strength,    Admixture, Wt.                  Mix (Hrs)  % of    Mix  percent of cement                      Initial Final                                   Within-group plain mix    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    19.  triethanolamine,                      -5/8    -3/4 108   104   101         0.01    20.  triethanolamine,                      -1/2    -7/8 110   107   107         0.025    21.  triethanolamine,                      -1/4    -5/8 109   107   107         0.05    22.  triethanolamine,                      +1/8    -1/4 110   105   105         0.10    ______________________________________

Data in Table VIII, obtained under the same conditions, show beneficialeffects of another adduct and how such adducts are additive inaccelerating effect when combined with triethanolamine or analkanolamine acid.

                  TABLE VIII    ______________________________________                  Time of                  Set Relative                  To Plain   Compressive Strength,    Admixture, Wt.                  Mix (Hrs)  % of    Mix  percent of cement                      Initial Final                                   Within-group plain mix    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    19.  di(hydroxyethyl)-                      +1/8    -1/8 109   118   109         β-amino-         propionitrile, 0.05    24.  di(hydroxyethyl)-                      -1/4    -3/4 103   117   108         β-aminopro-         pionitrile, 0.05 +         triethanolamine,         0.01    25.  di(hydroxyethyl)-                      -3/4    -7/8 111   122   110         β-aminopro-         pionitrile, 0.05 +         bicine, 0.01    ______________________________________

In this context it may be noted that bicine(N,N-di(hydroxyethyl)glycine) is more effective than triethanolamine, bycomparing data of Mix 24 with data of Mix 25.

The manner in which components within the scope of this invention mayadvantageously be combined into low-dosage but very effectivethree-component systems is further illustrated in Table IX. In this caseanother alkanolamine is employed, namelytetra(hydroxyethyl)ethylenediamine (THEED), which is an example of alarger class of hydroxyethyl-substituted diamines which are effective.

                  TABLE IX    ______________________________________                    Time of Set                    Relative to                             Compressive                    Plain Mix                             Strength, % of                    (Hrs)    Within-group    Mix  Admixture, Wt percent of                          Initial Final                                       plain mix    No.  cement on solid basis                          Set     Set  1-day    ______________________________________    26.  THEED, 0.025     -1/8    -3/8 110    27.  THEED, 0.025 +   -1/2    -1   115         triethanolamine, 0.015    28.  THEED, 0.025 +   -1 1/8  -1 5/8                                       154         triethanolamine, 0.015 +         NaCNS, 0.10    ______________________________________

It may be seen from data of Table IX that highly effective acceleratingadmixtures may be obtained by combinations at remarkably low totaldosage, in this case 0.14 weight percent of cements.

Data in Table X, Part A illustrate how a three-component admixture ofthis invention advantageously improves the accelerating effect of atwo-component subsystem; Table X, Part B, illustrates how usefulthree-component admixtures are still obtained when diethanolamine issubstituted for triethanolamine; and Table X, Part C, show incorresponding three-component systems that sodium salts are in somerespects less effective than corresponding calcium salts, but stillyield useful admixtures.

                  TABLE X    ______________________________________                    Time of Set                    Relative To                             Compressive                    Plain Mix                             Strength, % of                    (Hrs)    Within-group    Mix  Admixture, Wt percent of                          Initial Final                                       plain mix    No.  cement on solid basis                          Set     Set  1-day 3-days    ______________________________________    Part A    29.  NaNO.sub.3, 0.50 +                          -1 1/8  -1 1/2                                       145   112         NaCNS. 0.05 +         triethanolamine, 0.01    30.  NaNO.sub.3, 0.50 +                          -7/8    -1 3/8                                       137   111         NaCNS, 0.05    PART B    31.  NaNO.sub.3, 0.50 +                          -3/4    -1 1/4                                       129   109         NaCNS, 0.05 +         diethanolamine, 0.01    PART C    32.  Ca(NO.sub.3).sub.2,2.00 +                          -1 7/8  -2 3/8                                       151   140         Ca(CNS).sub.2, 0.20 +         triethanolamine, 0.04    33.  NaNO.sub.3, 2.00 +                          -3/4    -2   174   115         NaCNS, 0.20 +         triethanolamine, 0.04    ______________________________________

Tests discussed above indicate that sodium nitrate may be used inthree-component admixtures of the type here considered, in lieu ofcalcium nitrate. It has also been shown as indicated in Table XI that amixture of calcium and magnesium nitrates, prepared by treatment ofdolomite with nitric acid, and hereinbelow designated DOLNIT may also beadvantageously used. Data of Table XI also show the advantages of thethree-component admixture relative to selected one- and two-componentsubsystems. These tests were conducted in the same manner and under thesame conditions as those previously discussed.

                  TABLE XI    ______________________________________                  Time of                  Set Relative                  To Plain   Compressive Strength,    Admixture, Wt.                  Mix (Hrs)  % of    Mix  percent of cement                      Initial Final                                   Within-group plain mix    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    34.  NaCNS, 0.20  -15/8   -2   114   121    92    35.  DOLNIT, 2.00 -11/4   -13/4                                    90   108    95    36.  NaCNS, 0.20 +                      -15/8   -21/4                                   123   122   101         DOLNIT, 2.00    37.  NaCNS, 0.20 +                      -3/4    -21/8                                   130   131   104         DOLNIT, 2.00 +         triethanolamine,         0.04    ______________________________________

Similar data, using calcium nitrate, and bicine in lieu oftriethanolamine, and obtained under similar conditions, are shown inTable XII.

                  TABLE XII    ______________________________________                  Time of                  Set Relative                  To Plain   Compressive Strength,    Admixture, Wt.                  Mix (Hrs)  % of    Mix  percent of cement                      Initial Final                                   Within-group plain mix    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    38.  Ca(NO.sub.3).sub.2, 0.50                      -1/4    -7/8 101   108   104    39.  Ca(NO.sub.3).sub.2, 0.50 +                      -1 1/2  -2 1/8                                   117   115   112         bicine, 0.01    40.  Ca(NO.sub.3).sub.2, 0.50 +                      -1 3/4  -2 1/4                                   142   123   115         bicine, 0.01 +         NaCNS, 0.05    ______________________________________

Data of Table XIII illustrates the kinds of benefits secured when sodiumthiosulfate, Na₂ S₂ O₃, is employed as such, or together with NaCNS inadmixture systems of the type here considered. Test conditions were thesame as before.

                  TABLE XIII    ______________________________________                Time of                Set Relative                To Plain Compressive Strength,    Admixture, Wt Mix (Hrs)  % of    Mix  percent of cement                      Initial Final                                   Within-group plain mix    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    41.  NaNO.sub.3, 0.15 +                      -3/4    -3/4 115   102   102         triethanolamine,         0.01 + Na.sub.2 S.sub.2 O.sub.3,         0.15    42.  NaNO.sub.3, 0.15 +                      -7/8    -1 1/8                                   131   119   111         triethanolimine,         0.01 + Na.sub.2 S.sub.2 O.sub.3,         0.15 + NaCNS,         0.025    ______________________________________

Supplemental tests under the same conditions but with higher dosages ofnitrate and thiosulfate salts gave results as shown in Table XIV. Thesedata indicate that the alkanolamino acid, bicine, may be substituted fortriethanolamine in these systems, with no sacrifice to acceleration oftime of set of the concretes.

                  TABLE XIV    ______________________________________                Time of                Set Relative                To Plain Compressive Strength,    Admixture, Wt Mix (Hrs)  % of    Mix  percent of cement                      Initial Final                                   Within-group plain mix    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    43.  Ca(NO.sub.3).sub.2, 0.25 +                      -5/8    -7/8 107   107   103         Na.sub.2 S.sub.2 O.sub.3, 0.25    44   Ca(NO.sub.3).sub.2, 0.25 +                      -1 1/8  -1 3/8                                   112   112   109         Na.sub.2 S.sub.2 O.sub.3, 0.25 +         triethanolamine,         0.01    45.  Ca(NO.sub.3).sub.2, 0.25 +                      -1 1/8  -1 2/8                                   107   110   102         Na.sub.2 S.sub.2 O.sub.3, 0.25 +         bicine, 0.01    ______________________________________

It is within the scope of the invention to incorporate in the cementmixes as herein provided other admixtures known in the art for theexpress purpose for which they are normally employed. It is also withinthe scope of the invention to employ the accelerating system hereinprovided with known set retarders, such as lignosulfonates, sucrose,glucosaccharides and the like, to secure the benefits of these materialsbut with less retardation. Further with regard to admixtures known inthe art the American Concrete Institute Committee 201 on chloridecorrosion resistance has recommended (Concrete Construction, Vol. 27, p.777, 1982) that the maximum level of water soluble chloride ion (Cl⁻) tobe used for pre-stressed concrete applications, an application whichplaces the most stringent requirements for corrosion prevention, be0.06%. It has been found that thiocyanate replaced by chloride at 0.05%provides comparable performance when added to a fixed level of nitratesalt and alkanolamine, as illustrated by data in Table XV, wherein thedata were obtained at room temperature and under the conditionspreviously described.

                  TABLE XV    ______________________________________                Time of                Set Relative                To Plain Compressive Strength,    Admixture, Wt Mix (Hrs)  % of    Mix  percent of cement                      Initial Final                                   Within-group plain mix    No.  on solid basis                      Set     Set  1-day 7-days                                               28-days    ______________________________________    46.  Ca(NO.sub.3).sub.2, 0.25 +                      -1      -1/28                                   106   108   107         triethanolamine,         0.01    47.  Ca(NO.sub.3).sub.2, 0.25 +                      -1 3/8  -1 6/8                                   117   121   110         triethanolamine,         0.01 + CaCl.sub.2,         0.05    48.  Ca(NO.sub.3).sub.2, 0.25 +                      -3/8    -2   117   117   108         triethanolamine,         0.01 + NaCNS,         0.05    ______________________________________

Data in Table XV, comparing Mix 47 to Mix 48, show that in this contextand at these low dosages, the CaCl₂ is approximately as effective as thethiocyanate, in terms of promoting acceleration of setting andenhancement of compressive strength.

In complex admixture systems containing nitrates, thiocyanatestriethanolamine and other amines, it has been found that increasing theamount and proportion of triethanolamine within the dosage range inwhich it normally accelerates, surprisingly, decreases the accelerationof the composite admixture as shown in data of XVII below. All testconditions were the same as previously described. The effect is shown insystems containing tetra(hydroxyethyl)ethylenediamine (THEED) and ananalog thereof, namely, triethoxylated ethylenediamine.

                  TABLE XVI    ______________________________________                    Time of Set                    Relative To                             Compressive                    Plain Mix                             Strength, % of                    (Hrs)    Within-group    Mix  Admixture, Wt percent of                          Initial Final                                       plain mix    No.  cement on solid basis                          Set     Set  1-day    ______________________________________    49.  NaNO.sub.3, 0.25 +                          -1 1/8  -1 1/8                                       113         NaCNS, 0.025 +         THEED, 0.038 +         triethanolamine, 0.005    50   NaNO.sub.3, 0.25 +                          -1 1/8  -1 1/8                                       117         NaCNS, 0.025 +         THEED, 0.039 +         triethanolamine, 0.01    51.  NaNO.sub.3, 0.15 +                          -1 1/8  -1 1/4                                       115         NaCNS, 0.042 +         triethoxylated ethylene         diamine, 0.023 +         triethanolamine, 0.006    52.  NaNO.sub.3, 0.15 +                          -7/8    -1 1/2                                       124         NaCNS, 0.042 +         triethoxylated ethylene         diamine, 0.023 +         triethanolamine, 0.010    ______________________________________

Further data pertaining to systems containing a nitrate and athiocyanate with and without an alkanolamine or alkanolamino acid,obtained under the same test conditions as previously described, exceptthat a cement content of 517 pounds per cubic yard (307 kg/m³) was used,are shown in Table XVII below.

                  TABLE XVII    ______________________________________                              Compressive                    Time of Set                              Strength                    Relative To                              % of                    Plain Mix Within-group                    (Hrs)     plain mix    Mix  Admixture, Wt percent of                          Initial Final 1-   3-    No.  cement on solid basis                          Set     Set   day  days    ______________________________________    53.  Ca(NO.sub.3).sub.2, 0.50 +                          -1 1/8  -3/8  110  122         NaCNS, 0.10    54.  Ca(NO.sub.3).sub.2, 0.50 +                          -1 4/8  -1 4/8                                        119  119         NaCNS, 0.10 +         triethanolamine, 0.01    55.  Ca(NO.sub.3).sub.2, 0.50 +                          -1 6/8  -1 7/8                                        121  126         NaCNS, 0.10 +         di(hydroxyethyl)-β-amino-         propionic acid, 0.02    56.  Ca(NO.sub.3).sub.2, 0.50 +                          -1 4/8  -1 6/8                                        123  126         NaCNS, 0.10 +         bicine, 0.01    57.  Ca(NO.sub.3).sub.2, 0.50 +                          -1 3/8  -1 3/8                                        107  116         NaCNS, 0.10 +         N-hydroxyethylisopro-         panolamine, 0.01    58.  Ca(NO.sub.3).sub.2, 0.50 +                          -1 3/8  -1 3/8                                        103  110         NaCNS, 0.10 +         diethoxylated hydrazine,         0.02    59.  Ca(NO.sub.3).sub.2,0.50 +                          -1 2/8  -1 4/8                                        112  116         NaCNS, 0.10 +         diisopropanolamine,         0.01    60.  Ca(NO.sub.3).sub.2, 0.50 +                          -1 1/8  -1 3/8                                        106  124         NaCNS, 0.10 +         N-hydroxyethyldiisopro-         panolamine, 0.01    ______________________________________

Data in Table XVII illustrate how a variety of materials within thescope of this invention may advantageously be added at very smalldosages to a fixed base of nitrate plus thiocyanate to secure increasedacceleration of setting times. Some of the additions are beneficial tocompressive strength of the concretes and some are not. However, thecompressive strength levels are acceptable in all cases.

Data in Table XIII below were secured under the same test conditions,including the same brand of cement and the same cement content, exceptthat the tests were conducted at 50° F. (10° C.). The same base mixtureof nitrate and thiocyanate was employed, as shown.

                  TABLE XIII    ______________________________________                    Time of Set                    Relative To                             Compressive                    Plain Mix                             Strength, % of                    (Hrs)    Within-group    Mix  Admixture, Wt percent of                          Initial Final                                       plain mix    No.  cement on solid basis                          Set     Set  1-day    ______________________________________    61.  Ca(NO.sub.3).sub.2, 0.50 +                          -2 3/8  -3   130         NaCNS, 0.10    62   Ca(NO.sub.3)hd 2,0.50 +                          -3 3/8  -4 1/2                                       161         NaCNS, 0.10 +         triethanolamine, 0.01    63.  Ca(NO.sub.3).sub.2, 0.50 +                          -3 1/8  -4   153         NaCNS, 0.10 +         di(hydroxyethyl)-β-amino-         propionic acid, 0.02    64.  Ca(NO.sub.3).sub.2, 0.50 +                          -3 1/8  -4 2/8                                       157         NaCNS, 0.10 +         bicine, 0.01    65.  Ca(NO.sub.3).sub.2, 0.50 +                          -2 1/8  -2 2/8                                       136         NaCNS, 0.10 +         diethoxylated hydrazine,         0.02    66.  Ca(NO.sub.3).sub.2, 0.50 +                          -2 1/8  -2 2/8                                       137         NaCNS 0.10 +         N-hydroxyethyldiisopro-         panolamine, 0.01    ______________________________________

Data in Table XIII show very significant accelerations may be obtainedat low temperatures by these admixture combinations, with thealkanolamino acids being more nearly comparable to triethanolamine inthis context. Effects of the alkanolamino acid, bicine, employed aloneare significantly beneficial as shown in Table XIX wherein testconditions were the same as before:

                  TABLE XIX    ______________________________________                Time of    Admixture,  Set Relative To                            Compressive Strength,    Wt percent  Plain Mix (Hrs)                            % of    Mix  of cement  Initial Final Within-group plain mix    No.  on solid basis                    Set     Set   1-day 7-days                                              28-days    ______________________________________    67.  bicine, 0.01   -7/8    116   112   108    68.  bicine, 0.025  -5/8    108   111   107    69.  bicine, 0.05   0       113   111   106    70.  bicine, 0.10   -1 3/8  107   115   109    ______________________________________

Corresponding data for the alkanolamino acid,N,N-di(hydroxyethyl)aminomethyl succinic acid, monosodium salt, (DAMSA)obtained under the same conditions, and employed alone, are shown inTable XXI.

                  TABLE XX    ______________________________________                 Time of    Admixture,   Set Relative To                             Compressive Strength,    Wt percent   Plain Mix (Hrs)                             % of    Mix  of cement   Initial Final Within-group plain mix    No.  on solid basis                     Set     Set   1-day 7-days                                               28-days    ______________________________________    71.  DAMSA, 0.01     -1/8    112   106   112    72.  DAMSA, 0.025    -3/8    125   111   117    73.  DAMSA, 0.05     -3/8    122   108   124    74.  DAMSA, 0.10     -4/8    131   122   125    ______________________________________

While the invention has been described with reference to certainpreferred embodiments thereof, those skilled in the art will appreciatethat certain modifications and substitutions can be made withoutdeparting from the spirit of the invention. It is intended, therefore,that the invention be limited only by the scope of the claims whichfollow.

What is claimed is:
 1. A hydraulic cement mix comprising hydrauliccement, aggregate, sufficient water to effect hydraulic setting of thecement, and an admixture comprising a composition or a mixture ofcompositions selected from the group consisting of alkali, ammonium andalkaline earth salts of thiocyanic acid, and water soluble thiosulfates;a composition or a mixture of compositions selected from the group ..comprising.!. .Iadd.consisting of .Iaddend.alkanolamine; and . .relatedwater soluble alkanolamines and.!. alkanolamino acids; and a compositionor a mixture of compositions selected from the group . .comprising.!..Iadd.consisting of .Iaddend.alkali and alkaline earth salts of nitricacid; said additive being present in an amount sufficient to acceleratethe rate of hardening of said hydraulic cement mix and to increase itscompressive strength after hardening.
 2. A hydraulic cement mix inaccordance with claim 1 wherein said hydraulic cement comprises portlandcement. . .3. A hydraulic cement mix in accordance with claim 1 whereinsaid salts of thiocyanic acid are sodium, potassium, ammonium andcalcium thiocyanate; said soluble thiosulfates are sodium, potassium,ammonium, calcium and magnesium thiosulfates; said alkanolamines arediethanolamine and triethanolamine; said alkanolamino acids are bicineand di(hydroxyethyl)-β-propionic acid; a said related solublealkanolamine is tetra(hydroxyethyl)ethylenediamine; and said salts ofnitric acid are sodium, potassium, calcium, magnesium and ammoniumnitrates..!. . .4. A hydraulic cement mix in accordance with claim 1wherein said salt of thiocyanic acid is present in an amount from about0.01% to about 2.50% based on the weight of the cement; saidalkanolamine is present in an amount from 0.005% to about 0.08% based onthe weight of the cement; said salt of nitric acid is present in anamount from about 0.05% to about 2.00% based on the weight of thecement; said alkanolamino acid is present from about 0.005% to 0.10%based on weight of cement; and said thiosulfate salt is present in anamount from about 0.05% to about 2.00% based on weight of cement..!. 5.A hydraulic cement mix in accordance with claim 1 wherein said salt ofthiocyanic acid is present in an amount from about 0.025% to about0.50%; said alkanolamine from about 0.005% to about 0.02%; and said saltof nitric acid from about 0.10% to about 1.00%, based on the weight ofthe cement.
 6. A hydraulic cement mix in accordance with claim 1 whereinsaid salt of thiocyanic acid is sodium thiocyanate.
 7. A hydrauliccement mix in accordance with claim 1 wherein said salt of nitric acidis sodium nitrate.
 8. A hydraulic cement mix in accordance with claim 1wherein said salt of nitric acid is calcium nitrate.
 9. A hydrauliccement mix in accordance with claim 1 wherein said salt of nitric acidis a mixture of sodium nitrate and calcium nitrate. A hydraulic cementmix in accordance with claim 1 wherein said salt of nitric acid is amixture of magnesium nitrate and calcium nitrate.
 11. A hydraulic cementmix in accordance with claim 1 wherein said alkanolamine istriethanolamine.
 12. A hydraulic cement mix in accordance with claim 1wherein said alkanolamine is diethanolamine.
 13. A hydraulic cement mixin accordance with claim 1 wherein said thiosulfate salt is sodiumthiosulfate.
 14. A hydraulic cement mix in accordance with claim 1wherein said thiosulfate salt is calcium thiosulfate.
 15. A hydrauliccement mix in accordance with claim 1 wherein said . .water soluble.!.alkanolamino acid is bicine.
 16. A hydraulic mix in accordance withclaim 1 wherein said . .water soluble.!. alkanolamino acid isdi(hydroxyethyl)-β-aminopropionic acid.
 17. A hydraulic mix inaccordance with claim 1 wherein said . .water soluble.!. alkanolaminoacid is di(hydroxyethyl)-β-amino-α-methylpropionic acid.
 18. A hydraulicmix in accordance with claim 1 wherein said alkanolamino acid isN,N-di(hydroxyethyl)aminomethyl succinic acid.
 19. A hydraulic cementmix in accordance with claim 1 wherein said . .water soluble.!.alkanolamine is tetra(hydroxyethyl)ethylenediamine.
 20. A process foraccelerating the hardening of hydraulic cement mixes which includessequentially adding hydraulic cement, aggregate in an amount up to 80%by weight based on total weight of said cement mix, and sufficient waterto effect hydraulic setting of the cement, comprising incorporating anadmixture comprising mixtures of(a) a composition selected from thegroup . .comprising.!. .Iadd.consisting of .Iaddend.ammonium, alkali,and alkaline earth salts of thiocyanic acid, and mixtures thereof; andwater soluble thiosulfates that may be substituted in whole or in partfor the thiocyanates; and (b) an alkanolamine; and water solublealkanolamino acids, substituted in whole or part for the alkanolamine;(c) a composition selected from the group . .comprising.!..Iadd.consisting of .Iaddend.ammonium, alkali, and alkaline earth saltsof nitric acid, and mixtures thereof;said additive being incorporated inan amount sufficient to accelerate the rate of hardening of saidhydraulic cement mix and to increase its compressive strength afterhardening.
 21. A process in accordance with claim 20, wherein saidhydraulic cement comprises portland cement. . .22. A process inaccordance with claim 20, wherein the thiocyanate is present in anamount from about 0.01% to about 0.50%; the alkanolamine is present inan amount from about 0.005% to about 0.08%; and the nitrate is presentin an amount from about 0.05% to about 2.00% based on the weight of thecement in the mix; said soluble alkanolamino acid is present from about0.005 to 0.10% based on weight of cement; and said thiosulfate salt ispresent in an amount from about 0.05% to about 2.00% based on weight ofcement..!.
 23. A process in accordance with claim 20 wherein thethiocyanate is sodium thiocyanate.
 24. A process in accordance withclaim 20 wherein the alkanolamine is triethanolamine.
 25. A process inaccordance with claim 20 wherein the nitrate is sodium nitrate.
 26. Aprocess in accordance with claim 20 wherein the nitrate is calciumnitrate.
 27. A process in accordance with claim . .17.!. .Iadd.20.Iaddend.wherein the nitrate is a mixture of sodium nitrate and calciumnitrate.
 28. A process in accordance with claim . .17.!. .Iadd.20.Iaddend.wherein the nitrate is a mixture of magnesium nitrate andcalcium nitrate.
 29. A process in accordance with claim . .17.!..Iadd.20 .Iaddend.wherein said thiosulfate salt is sodium thiosulfate.30. A process in accordance with claim . .17.!. .Iadd.20.Iaddend.wherein said thiosulfate salt is calcium thiosulfate.
 31. Aprocess in accordance with claim . .17.!. .Iadd.20 .Iaddend.wherein saidwater soluble . .of.!. alkanolamino acid is bicine.
 32. A process inaccordance with claim . .17.!. .Iadd.20 .Iaddend.wherein said watersoluble alkanolamino acid is di(hydroxyethyl)-β-aminopropionic acid. 33.A process in accordance with claim . .17.!. .Iadd.20 .Iaddend.whereinsaid . .water soluble.!. alkanolamine istetra(hydroxyethyl)ethylenediamine. .Iadd.34. A hydraulic cement mix inaccordance with claim 1 whereinsaid composition or mixture ofcompositions selected from the group consisting of alkali, ammonium andalkaline earth salts of thiocyanic acid and water soluble thiosulfatesis present in an amount from about 0.01% to about 0.50% based on theweight of the cement; said composition or mixture of compositionsselected from the group consisting of alkanolamine and alkanolaminoacids is present in an amount from about 0.005% to about 0.10% based onthe weight of the cement, with the proviso that alkanolamines, whenpresent, are present in an amount from about 0.005% to about 0.08% basedon the weight of the cement; and said composition or mixture ofcompositions selected from the group consisting of alkali and alkalineearth salts of nitric acid is present in an amount from about 0.05% toabout 2.00% based on the weight of the cement. .Iaddend. .Iadd.35. Ahydraulic cement mix in accordance with claim 34 wherein thiocyanate ispresent in an amount from about 0.01% to about 0.50% based on the weightof the cement, and wherein alkanolamine is present in an amount fromabout 0.005% to about 0.08% based on the weight of the cement. .Iaddend..Iadd.36. A process in accordance with claim 20 wherein said compositionselected from the group consisting of ammonium, alkali, and alkalineearth salts of thiocyanic acid, and mixtures thereof, and water solublethiosulfates that may be substituted for the thiocyanates is present inan amount from about 0.0% to about 0.50% based on the weight of thecement; said alkanolamine and water soluble alkanolamino acidssubstituted for the alkanolamine are present in an amount from about0.005% to about 0.10% based on the weight of the cement, with theproviso that alkanolamine, when present, is present in an amount fromabout 0.005% to about 0.08% based on the weight of the cement; and saidcomposition selected from the group consisting of ammonium, alkali, andalkaline earth salts of nitric acid, and mixtures thereof is present inan amount from about 0.05% to about 2.00% based on the weight of thecement. .Iaddend. .Iadd.37. A process in accordance with claim 36wherein thiocyanate is present in an amount from about 0.01% to about0.50% based on the weight of the cement, and wherein alkanolamine ispresent in an amount from about 0.005% to about 0.08% based on theweight of the cement. .Iaddend. .Iadd.38. A hydraulic cement mixcomprising hydraulic cement, aggregate, sufficient water to effecthydraulic setting of the cement, and an admixture comprising: a)composition or a mixture of compositions selected from the groupconsisting of alkali, ammonium and alkaline earth salts of thiocyanicacid, and water soluble thiosulfates, wherein said salts of thiocyanicacid are sodium, potassium, ammonium and calcium thiocyanate; and saidsoluble thiosulfates are sodium, potassium, ammonium, calcium andmagnesium thiosulfates; b) a composition or a mixture of compositionsselected from the group consisting of alkanolamine and alkanolaminoacids, wherein said alkanolamines are diethanolamine, triethanolamine ortetra(hydroxyethyl)ethylenediamine; and said alkanolamino acids arebicine and N,N-di(hydroxyethyl)-β- aminopropionic acid; and c) acomposition or a mixture of compositions selected from the groupconsisting of alkali, ammonium and alkaline earth salts of nitric acid,wherein said salts of nitric acid are sodium, potassium, calcium,magnesium and ammonium nitrates;said admixture being present in anamount sufficient to accelerate the rate of hardening of said hydrauliccement mix and to increase its compressive strength after hardening..Iaddend.